Kaoru Kumada, who prefers the self-given nickname "Buta Gorilla" (also Butagorira or Goril·la), adopted this derogatory term due to embarrassment over his traditionally feminine given name. His father Kumahachi chose "Kaoru" to avoid another unusual name like his own. Kaoru only reconciled with his name after a time-travel encounter with ancestors revealed his father's intentions.

An overweight elementary school bully, he initially antagonizes the robot Korosuke and classmates like Tongari. He wears a blue-striped t-shirt, brown pants, and a blue cap. Academically weak except in physical education, he fears green caterpillars and frequently boasts about never getting sick, though he consistently develops fevers during mathematics exams.

Unlike typical bully characters, he actively helps in his family's vegetable shop, owned by his father Kumahachi, and possesses extensive vegetable knowledge reflecting passion for the business. His mother is Sayuri.

His character evolves from a straightforward bully to a dimwitted but kind-hearted comic relief figure. While he continues teasing Korosuke, he also demonstrates hidden care for the robot. His troublemaking often results from unintentional mistakes rather than malice.

He develops romantic feelings for Sakurai Taiko, a sweet-natured transfer student whose mother runs a public bathhouse. Though Taiko eventually moves to either Hokkaido or Niigata, she occasionally visits and appears to reciprocate his affection somewhat. His interactions with Tongari remain complex, blending friendship with ongoing bullying tendencies.